Communication pubs.acs.org/JACS
Role of Coherent Low-Frequency Motion in Excited-State Proton Transfer of Green Fluorescent Protein Studied by Time-Resolved Impulsive Stimulated Raman Spectroscopy Tomotsumi Fujisawa,†,∥,⊥ Hikaru Kuramochi,†,⊥ Haruko Hosoi,‡ Satoshi Takeuchi,†,§ and Tahei Tahara*,†,§ †
Molecular Spectroscopy Laboratory, RIKEN, and §Ultrafast Spectroscopy Research Team, RIKEN Center for Advanced Photonics (RAP), 2-1 Hirosawa, Wako 351-0198, Japan ‡ Department of Biomolecular Science, Faculty of Sciences, Toho University, 2-2-1 Miyama, Funabashi 274-8510, Japan S Supporting Information *
transfer (ESPT), producing the green-fluorescent deprotonated chromophore (I form) in the excited state (Figure 1A) on the
ABSTRACT: Green fluorescent protein (GFP) from jellyfish Aequorea victoria, an essential bioimaging tool, luminesces via excited-state proton transfer (ESPT) in which the phenolic proton of the p-hydroxybenzylideneimidazolinone chromophore is transferred to Glu222 through a hydrogen-bond network. In this process, the ESPT mediated by the low-frequency motion of the chromophore has been proposed. We address this issue using femtosecond time-resolved impulsive stimulated Raman spectroscopy. After coherently exciting lowfrequency modes (
